The overall objective of this clinical trial is to determine the ability of bispecific murine monoclonal antibody (BsMAb) therapy to induce antitumor responses through recruitment and activation of relevant effector cells to tumor in patients with advanced, metastatic breast carcinoma. This objective is predicated upon the hypothesis that BsMAb targeting tumor and the Fcy receptor expressed by large granular lymphocytes (LGLs) and macrophages will promote stable in vivo binding between effector and target cells. The maximally tolerated BsMAb dose has been identified in a Phase IA trial then modified in the course of this trial, and will permit the testing of this hypothesis in this Phase IB/II trial. The study of other factors which may be required to achieve optimal accumulation of these effectors at tumor sites will permit the design of subsequent clinical trials which address such factors regulating this process.